This application is a national phase application under 35 U.S.C. §371 of International Application No. PCT/US2014/037342, filed May 8, 2014, which claims the benefit of U.S. Provisional Patent Application No. 61/821,181, filed May 8, 2013, the entirety of each of which is incorporated herein by reference.
1. Field of the Invention
The present invention relates generally to the field of medicinal chemistry and medicine. More particularly, it concerns STAT6 inhibitors.
2. Description of Related Art
Asthma patients have elevated levels of the cytokines interleukin 4 (IL-4) and IL-13 in their airways, which result in mucus production, airway hyperresponsiveness (AHR), eosinophil recruitment, T-Helper cell 2 (Th2) activation, resulting in immunoglobulin class switching to IgE, and inflammation (reviews 1-3). These two cytokines signal through a common receptor, the alpha chain of the IL-4 receptor (IL-4Rα). On cytokine binding, tyrosine residues on the receptor are phosphorylated by JAK1, JAK3, or Tyk2. Signal transducer and activator of transcription 6 (STAT6), via its Src homology 2 (SH2) domain, is recruited to the phosphotyrosine residues and is then phosphorylated on Tyr641. STAT6 then dimerizes via reciprocal SH2 domain-pTyr641 interactions, translocates to the nucleus, and participates in the expression of genes leading to asthma and airway hyperresponsiveness (AHR). Elevated STAT6 levels have been found in the bronchial epithelium of asthma patients (Mullings et al. 2001). Stat6 knockout mice do not develop airway hyperresponsiveness (AHR) or lung pathology associated with asthma regardless of the asthmatic stimuli applied (Darcan-Nicolaisen et al. 2009). Taken together, these results support the hypothesis that inhibiting the activity of STAT6 is a beneficial modality for asthma treatment (Kasaian, M. T. et al. 2008; Popescu, F. D. 2003; Chiba, Y. et al. 2009; McCusker, C. T. et al. 2007; Nagashima, S. et al. 2009; Nagashima, S. et al. 2008; Nagashima, S. et al. 2007; Ohga. K. et al. 2008; Stolzenberger. S. et al. 2001; Oh, C. K. et al. 2010).
STAT6 activity has been inhibited by small molecules (Nagashima, S. et al. 2009; Nagashima, S. et al. 2008; Nagashima, S. et al. 2007; Ohga, K. et al. 2008; Chiba, Y. et al. 2009), siRNA (Darcan-Nicolaisen, Y. et al. 2009), decoy oligonucleotides,15 and antibodies (Walsh, G. M. 2012; Blease, K. 2008). Nagashima et al. identified a small molecule hit by screening a company library for the ability to inhibit a STAT6 reporter gene (Nagashima, S. et al. 2007), an assay that drove lead optimization leading to AS 1571499 (FIG. 2). Further development led to AS 1617612, also known as YM 341619 (Nagashima, S. et al. 2008), and then to AS 1810722 (Nagashima et al. 2009). Zhou et al. screened libraries and identified (R)-76 and its synthetic derivative (R)-84 that bind to STAT6 and prevent phosphorylation on Tyr641 (FIG. 2). To date, none of these materials have proved to be effective at treating STAT6-mediated diseases.
A number of potential phosphopeptide compounds have been prepared but few have the potential to advance to a clinical drug candidate. Stolzenberger et al.; Stolzenberger, S. et al. 2001, prepared a phosphopeptide derived from Tyr631 of IL-4Rα, a docking site for STAT6, coupled to the antennapedia cell penetration sequence (AP/STAT6BP) (FIG. 3). IL-4 stimulation of STAT6 phosphorylation in RAMOS cells was inhibited at 5 and 10 μM, but recovered at 30 min. McCusker, et. al. (2007), reported that STAT-6-IP, a phosphopeptide derived from the phosphorylation site of STAT6, Tyr641, attached to a cell penetration sequence from TAT PT4 protein transduction domain (STAT-6-IP), inhibited in vitro IL-4 and IL-13 expression from splenocytes from mice challenged with ovalbumin (OVA) (FIG. 3). Importantly, in vivo intranasal administration inhibited OVA-induced lung inflammation and mucus production, eosinophil migration and AHR. The same group recently reported that intranasal administration of STAT-6-IP inhibited the same symptoms in a mouse asthma model induced by ragweed pollen (Wang, Y. et al. 2011). However, these materials are not likely to become commercial products for the treatment of asthma.
A few potential small molecular peptide mimetics have been explored that showed promise as potential STAT6 inhibitors. Small molecule peptide mimetics that target the SH2 domain of STAT6 have been reported in U.S. Pat. No. 6,426,331 and PCT Patent Application WO2001/083517. Although extensive structure-affinity relationship studies were reported, the synthesis of only one compound which was effective to inhibit STAT6 phosphorylation in intact cells was described (PM-241H, our nomenclature, FIG. 4). However, the synthesis of the compound was complicated and resulted in poor yields. Furthermore, that compound was not tested for any biological activity relating to STAT6. Clearly, there is a need for new STAT6 inhibitors.